The present invention relates generally to a technique for inspecting materials and testing material integrity. Particularly, the present technique relates to methods and apparatus for testing the integrity of rails in railroad systems using phased array based ultrasonic techniques.
Detecting the presence of defects in rails can assist maintenance technicians, for example, in predicting and mitigating the likelihood of rail malfunctions due to defects, for instance. By way of example, commonly occurring defects in the rail and/or railheads of railroad transportation systems are horizontal defects, transverse defects and bolthole defects. Horizontal defects, such as shelling and horizontal split-heads, are generally transverse and sometimes parallel to the longitudinal axis of the rail. Conversely, transverse defects are generally perpendicular to the longitudinal axis of the rail. Another general category of defects is bolthole defects, which generally occur near the boltholes of the rail. Under certain conditions, horizontal and transverse defects as well as bolthole defects can propagate under the fatigue of cyclic use. Unfortunately, these defects or cracks in the rail can increase the likelihood of failure or malfunction of the rail and/or railhead, leading to undesirable maintenance costs and downtimes, for instance.
In many instances, rail inspections are performed using an ultrasonic transducer mounted to an inspection vehicle. For example, one ultrasonic testing technique employs a single ultrasonic transducer attached to a sliding fixture, which, in turn, is mounted to a moving inspection vehicle. In another inspection method that is generally known as a “wheeled-probe system” an ultrasonic transducer is placed within a small diameter of a fluid filled inspection wheel that, in turn, is mounted to a moving inspection vehicle. In such a system, the fluid provides a medium for the ultrasonic waves to travel from the transducer and into the rail.
In traditional wheeled-probe systems, the time-to-flight, i.e., the period of time required for ultrasonic wave to leave the transducer, reflect from a base of the rail and return to the sensing device, is approximately 180 microseconds. Accordingly, to increase the likelihood that the transmitted wave returns to the sensing device, the speed of travel (i.e., scan speed) of the wheel-probed system is limited to approximately 35 miles per hour (mph). That is to say, if scan speeds exceed 35 mph, losses of reflected ultrasonic signals will dramatically increase, because the ultrasonic transducers will have traveled past the inspection area before the reflected ultrasonic signals can reach or return to the transducer. Hence, traditional testing techniques are limited at the speed at which testing can be performed. Unfortunately, limited testing speeds can lead to unwanted delays in track testing that, in turn, can lead to track closures, for instance.
Additionally, traditional techniques call for focusing and directing a generated beam by mounting the ultrasonic transducers at fixed angles with respect to the rails. Unfortunately, angularly maintaining the ultrasonic transducers with respect to the rail decreases the cross-section coverage area of the ultrasonic transducers. In turn, the probability of detecting oriented defects is also decreased, because of reduced area.
Thus, there exists a need for methods and apparatus for performing high-speed inspections to detect defects in the rails and to determine the integrity of such rails.